Question

Please describe the upstream molecular events that activate alpha, beta, and gamma subunits of G-proteins in a typical cell-signaling event. (please do not exceed more than 15 sentences in answer , thanks)

Answer 1

G-protein coupled receptor works under the influence of the desired ligand and the G-protein binding which comprises of the three subunit alpha, beta, and gamma. In the case of the cell signal transduction, even the ligand is bound to the GPCR and then the downstream signaling pathway is switched on. In this, the G-protein is bound to the GPCR and carry out the signaling by replacing the GDP bound G-protein in the alpha subunit with the GTP through the action of the Guanine Exchange Factor (GEF). This helps in the dissociation of the alpha subunit and the beta-gamma subunit which carry out the effective function by moving from the G-protein to the effector site and allow the signaling cascade to continue.

After the signaling has been stopped and the ligand has been removed then the GTPase Activating Protein (GAP) is overexpressed. This allows hydrolyzing the bound GTP into GDP and due to which all subunit again get into closure and then the protein again goes in the dormant stage that is the inactive form. The signaling cascade can run various function such as formation of the cAMP inside the cytosol by expressing the adenylate cyclase, opening of the ion channels, etc.